Vegetables in Containers

Why Grow your plants in Containers?

As housing density increases and more people are living in apartments or on blocks with limited outdoor areas, the need for container grown crops becomes obvious.

The advantages of container-growing of vegetables are many, but the biggest benefit is that people without access to garden beds can grow a range of crops, whether it is on a balcony, patio or other area.

Containers can either replace or supplement outdoor inground garden beds. They are particularly useful for herbs, or other crops where only one or two plants are required.

Container-grown crops can be moved to receive full sun, or to protect them from winds or pests. Crops may be grown at the start and end of the season indoors when outside conditions are too severe. Remember that a paved area such as a patio can become very hot if it is in full sun all day: this may be an advantage or a problem, depending on which crops you are trying to grow.

The decorative value of small or large containers filled with some of the more attractive plants should not be underestimated. Capsicums, coloured beet, rhubarb and tomatoes all make attractive displays.

Feeding and watering can be easily controlled in containers; weed problems are usually less and very often pests and diseases are less active.

Unfortunately container-grown vegetables usually yield less than similar plants grown in a good garden situation. This difference can be minimised with careful attention to feeding and watering however. Soils require mixing and fertilising and frequent attention is required.

Soil

The main requirement for satisfactory container-grown plants is the soil. This must be fertile and well-drained and, above all, it must remain friable and not compact.

Many commercial potting mixes are quite unsuitable for container-grown vegetables, due largely to their very varied ingredients often of totally unknown quality. Many of these mixes consist largely of fillers like Pine bark with any nutrient being quickly exhausted.

A good mixture that can be readily made is as follows:

1 part by volume each of garden loam

quality compost

coarse propagating sand

To each 35 litres by volume of the mixture add 80 grams of agricultural lime and 100 grams of a complete fertiliser, e.g. one with an NPK analysis of 6:6:6. Leaf crops will benefit from the addition of 15 grams of sulphate of ammonia to the mix. This is only a starting point, as regular additional feedings will still be required.

Containers

It is important that the container chosen is of suitable size for the crop to be grown: suggestions are given the table towards the end of this leaflet. The container must have plenty of drainage holes and should have a base of similar size to the top.

Large containers are those with a diameter greater than 45 cm and a depth of at least 30 cm; medium containers are from 20 cm diameter and 20 cm deep; while small containers are from 15 cm diameter and depth.

Outdoor raised beds are another type of container that can be used. These may be portable or permanent items. The principles for their use are essentially the same as for any other container.

Many kinds of containers can be purchased; the durable black plastic type is functional although more decorative types can be found. Containers can be made from old drums, barrels, buckets or anything that will hold sufficient soil and can be pierced to allow drainage.

Watering and feeding

The well-drained soil in the pot will require to be watered and fed regularly. Plants should be watered daily in warm periods; when conditions are cool, the soil should only be watered as it begins to dry.

Remember that the root run in a container is limited and the plants will require at least daily watering in warm weather to keep from growing rapidly. As they become larger, and their leaf area increases, so does their need for water become greater. Frequent watering will remove some of the soluble plant food from the soil. Regular small applications of plant food are therefore required, using products like Aquasol, Osmocote or Thrive. Leafy crops and the larger crops like tomatoes will require more frequent applications than smaller fruiting crops. Liquid manures or fertilisers are successful, provided adequate nutrients are in the soil in the first place. Weekly applications are required, usually as an addition to fortnightly side dressings of a dry fertiliser.

Filling the container

Before placing the soil in the container, ensure that the drainage holes are open. Place a layer of coarse mat erial like coarse gravel or pieces of broken pots to keep them open and to allow free drainage of the mixture.

Fill the container with soil mixture to just slightly below the top; allow for some settling as the soil is watered. Seeds or plants are planted in the container in the same way as you would outdoors.

Taller growing plants will need some form of support, usually a stake of some kind. This should be placed firmly in the pot before planting; tie the plant to the stake as it grows.

Clean containers

Whenever containers are re-used they should be thoroughly scrubbed clean, removing any plant or soil adhering to them. Sterilising the pots by using a formalin solution or a household bleach like White King, will help to prevent any diseases from being carried over to the new plants.

Re-using soil

The amount of soil left over after growing a vegetable crop in containers is quite considerable and its disposal often seems both wasteful and expensive. The obvious course is to re-use it.

However, soil should not be re-used without treatment. It will require a replacement of nutrients and organic matter, the removal of plant roots that may create infection and sterilisation.

Experience has shown that used soil is a good material to add to compost bins in thin layers and helps make a compost that is extremely useful in both the garden bed and soil mixes.

Principles of rotation should also be observed when reusing soil to avoid a build-up of disease.

Suggested container sizes for Vegetables

Crop

Container size

Comments

Artichoke, globe

Large and deep

Ornamental

Bean, climbing, and

dwarf French,

Medium or large

Climbing types prefer large containers.

Bean, perennial

Large

Beet, red, silver

Small to large

Medium

Large container will allow more plants.

Broccoli

Very large

Try the smaller Baby Bunching variety.

Brussels sprouts

Large

Cabbage

Medium

Medium containers for individual small-headed

varieties

Cabbage, Chinese

Small

Large containers for more than individual plants

Capsicum

Medium

Excellent crop for containers

Carrot

Deep

Not really suited to other than short varieties.

French Round is excellent

Celeriac

Medium

Celery

Medium

Requires constant moisture.

Cress

Any size

Thrives.

Cucumber

Large

Use bush varieties like Bush Crop.

Endive

Any size

Kale

Large

Attractive, especially variegated varieties

Kohl Rabi

Any size

Need large surface area for numerous plants.

Lettuce

Any size

Need large surface area for numerous plants.

Heavy constant feeding required.

Mustard

Shallow tray

New Zealand yam

Medium

Onion (shallots only)

Small to large

Small containers excellent for individual plants

of chives, garlic, shallots

Parsley

Medium

Potato

Large

Radish

Small to large

Use only round or short varieties.

Rhubarb

Large

Squash

Large

Bush varieties only

Spinach

Small

Tomato

Large

Pot progressively from small pot to a larger one.

Hydroponics

Another method of using containers is to do away with the soil and grow the crops in a medium with circulating nutrient. This is hydroponics.

Hydroponics is a system of growing plants in water to which are added exact amounts of nutrients. The roots are continually submerged in circulating water, the plants being supported in sterile soil, gravel, coarse sand or other mediums.

Hydroponics allows for exact control of the nutrients that plants receive, producing excellent crops. It is generally unsuited to root crops like carrot and parsnip, although good root crops have sometimes been produced.

Hydroponics is a specialist subject. Its rewards, however, may make it attractive to keen gardeners with a desire to produce crops without soil in containers. An excellent book on the subject can be found in our catalogue.